NHANES is the Institute's premier source for nationally representative data on the prevalence of heart, lung, blood, and sleep disorders, diseases, correlates, and risk factors. It is the only nationally representative survey with a clinical component. The Institute relies of the information derived from this study to establish priorities, to identify subgroups at high risk for disease and disability, and to track the efficacy and penetration of Institute educational and preventative efforts among U.S. citizens. It incorporates a unique combination of survey and physical exam in a travelling clinic, by virtue of which highly standardized measures of physical and descriptive information can be gleaned from U.S. citizens throughout the country.